Trail orders are extremely useful, much more so than simple stop loss orders. Are there any exchanges that offer trail orders?

Using a trail order, the stop price would track the market price as long as it goes in the same direction, but not if the market price moves in the opposite direction. For example, say BTC is bid 250 USD and I place a trail stop (sell) order for 10 USD below the bid price. Here's what happens if BTC moves:

start => my trail order will have a stop of 240

BTC bid 260 => my trail order will have a stop of 250 now

BTC bid 265 => stop 255

BTC bid back to 262 => stop 255 stays in place

BTC bid 268 => stop 258

BTC bid 263 => stop stays 258

BTC bid tunnels down to 255 => market SELL order triggered as soon as the bid went <=258

However, there's an important warning to be heeded: by placing trailing stop orders with any exchange, you expose yourself to very short-lived price spikes that are not reflected anywhere else. Here is a screenshot from Kraken where the three red dots represent trades triggered by the price falling by 25% for a minute, only to shoot back up immediately afterwards. The trailing stop didn't offer any protection here; on the contrary, it caused a loss.

This is simple to achieve with an API (offered by most exchanges) and a bot. It is not foolproof as rapid price movements may escape it, but it is probably good enough. However, I do not know of such bot.

Currently none for virtual currencies. You may want to contact each exchange you are comfortable with and ask them if/when they intend to install that. I have done similar with some FOREX programs ( using the pretend cash ) with success and have yet to see more than just straight buy/sell at this point. The virtual currency exchanges are still in their infancy and could use some prodding to get up to speed with the tools that FOREX traders currently have available.